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Versions: (draft-mohan-pwe3-mpls-eth-oam-iwk) 00 01 02 03 04 05 06 07 08 RFC 7023

     PWE3 Working Group                               Dinesh Mohan (Ed.)
     INTERNET-DRAFT                                     Nortel Networks
     Intended status: Proposed Standard
     Expires: June 2013                                Nabil Bitar (Ed.)
                                                                Verizon
     
                                                       Ali Sajassi (Ed.)
                                                                  Cisco
     
     
     
                                                      January 30, 2013
     
     
                        MPLS and Ethernet OAM Interworking
                     draft-ietf-pwe3-mpls-eth-oam-iwk-07.txt
     
     
     Abstract
     
     This document specifies the mapping of defect states between
     Ethernet Attachment Circuits (ACs) and associated Ethernet
     Pseudowires (PWs) connected in accordance to the PWE3 architecture
     to realize an end-to-end emulated Ethernet service. It standardizes
     the behavior of Provider Edges (PEs) with respect to Ethernet PW
     and AC defects.
     
     
     Status of this Memo
     
     This Internet-Draft is submitted in full conformance with the
     provisions of BCP 78 and BCP 79.
     
     Internet-Drafts are working documents of the Internet
     Engineering Task Force (IETF). Note that other groups may also
     distribute working documents as Internet-Drafts. The list of
     current Internet-Drafts is at
     http://datatracker.ietf.org/drafts/current/.
     
     Internet-Drafts are draft documents valid for a maximum of six
     months and may be updated, replaced, or obsoleted by other
     documents at any time.  It is inappropriate to use Internet-
     Drafts as reference material or to cite them other than as "work
     in progress."
     
     This Internet-Draft will expire on June 30, 2013.
     
     
     
     
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     Copyright Notice
     
     Copyright (c) 2013 IETF Trust and the persons identified as the
     document authors. All rights reserved.
     
     This document is subject to BCP 78 and the IETF Trust's Legal
     Provisions Relating to IETF Documents
     (http://trustee.ietf.org/license-info) in effect on the date of
     publication of this document. Please review these documents
     carefully, as they describe your rights and restrictions with
     respect to this document. Code Components extracted from this
     document must include Simplified BSD License text as described
     in Section 4.e of the Trust Legal Provisions and are provided
     without warranty as described in the Simplified BSD License.
     
     
     Table of Contents
     
        1. Specification of Requirements........................ 3
        2. Introduction......................................... 3
           2.1. Reference Model and Defect Locations............ 5
           2.2. Abstract Defect States.......................... 5
        3. Abbreviation and Terminology......................... 6
           3.1. Abbreviations................................... 6
           3.2. Terminology..................................... 7
        4. PW Status and Defects................................ 7
           4.1. Use of Native Service (NS) Notification......... 8
           4.2. Use of PW Status Notification for MPLS PSNs..... 8
           4.3. Use of BFD Diagnostic Codes..................... 9
           4.4. PW Defect States Entry and Exit Criteria........ 9
              4.4.1. PW Receive Defect State Entry and Exit..... 9
              4.4.2. PW Transmit Defect State Entry and Exit... 10
        5. Ethernet AC Defect States Entry and Exit Criteria .. 10
           5.1. AC Receive Defect State Entry and Exit......... 10
           5.2. AC Transmit Defect State Entry and Exit........ 12
        6. Ethernet AC and PW Defect States Interworking....... 12
           6.1. PW Receive Defect Entry Procedures............. 12
           6.2. PW Receive Defect Exit Procedures.............. 13
           6.3. PW Transmit Defect Entry Procedures............ 14
           6.4. PW Transmit Defect Exit Procedures............. 15
           6.5. AC Receive Defect Entry Procedures............. 15
           6.6. AC Receive Defect Exit Procedures.............. 16
           6.7. AC Transmit Defect Entry Procedures............ 16
           6.8. AC Transmit Defect Exit Procedures............. 17
        7. Security Considerations............................. 17
        8. IANA Considerations................................. 17
        9. Acknowledgments..................................... 17
     
     
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        10. References......................................... 18
           10.1. Normative References.......................... 18
           10.2. Informative References........................ 18
        11. Appendix A: Ethernet Native Service Management..... 19
     
     1. Specification of Requirements
     
     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
     "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
     this document are to be interpreted as described in [RFC2119].
     
     2. Introduction
     
     This document specifies the mapping of defect states between
     Ethernet Attachment Circuits (ACs) and associated Ethernet
     Pseudowires (PWs) connected in accordance to the PWE3 architecture
     [RFC3985] to realize an end-to-end emulated Ethernet service. This
     document augments the mapping of defect states between a PW and
     associated AC of the end-to-end emulated service in [RFC6310]. It
     covers the following Ethernet OAM (Operations, Administration and
     Maintenance) mechanisms and their interworking with PW OAM
     mechanisms:
     
          - Ethernet Continuity Check (CC) [802.1ag][Y.1731]
          - Ethernet Alarm Indication Signaling (AIS) and Remote Defect
            Indication (RDI) [Y.1731]
          - Ethernet Link OAM [802.3]
          - Ethernet Local Management Interface {E-LMI} [MEF16]
     
     Ethernet Link OAM [802.3] allows some Link defect states to be
     detected and communicated across an Ethernet Link. When an Ethernet
     AC is an Ethernet physical port, there MAY be some application of
     Ethernet Link OAM [802.3]. Further, E-LMI [MEF16] also allows for
     some Ethernet Virtual Circuit (EVC) defect states to be
     communicated across an Ethernet UNI where Ethernet UNI constitutes
     a single hop Ethernet Link (i.e. without any 802.1Q/.1ad compliant
     bridges in between). There may be some application of E-LMI [MEF16]
     for failure notification across single hop Ethernet AC in certain
     deployments that specifically do not support [802.1ag] and/or
     [Y.1731]. [Y.1731] and [802.1ag] based mechanisms are applicable in
     all types of Ethernet ACs. Ethernet Link OAM [802.3] and E-LMI
     [MEF16] are optional and their applicability is called out, where
     applicable.
     
     Native Service (NS) OAM MAY be transported transparently over the
     corresponding PW as user data. This is referred to as "the single
     
     
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     emulated OAM loop" mode per [RFC6310]. For Ethernet, as an example,
     802.1ag continuity check messages (CCMs) between two Maintenance
     End Points (MEPs) can be transported transparently as user data
     over the corresponding PW. At MEP locations, service failure is
     detected when CCMs are not received over an interval that is 3.5
     times the local CCM transmission interval. This is one of the
     failure conditions detected via CC. MEP peers can exist between
     Customer Equipment (CE) pairs (MEPs of a given Maintenance Entity
     Group (MEG) reside on the CEs), PE pairs (the MEPs of a given MEG
     reside on the PEs), or between the CE and PE (the MEPs of a given
     MEG reside on the PE and CE), as long as the MEG level nesting
     rules are maintained. It should be noted that Ethernet allows the
     definition of up to 8 MEG levels, each compromising of MEPs (Down
     MEPs and Up MEPs) and Maintenance Intermediate Points (MIPs). These
     levels can be nested or touching. MEPs and MIPs generate and
     process messages in the same MEG level. Thus, whenever in this
     document we refer to messages sent by a MEP or a MIP to a peer MEP
     or MIP, these MEPs and MIPs are in the same MEG level.
     
     When interworking two networking domains, such as native Ethernet
     and PWs to provide an end-to-end emulated service, there is need to
     identify the failure domain and location even when a PE supports
     both the NS OAM mechanisms and the PW OAM mechanisms. In addition,
     scalability constraints may not allow running proactive monitoring,
     such as CCMs with transmission enabled, at a PE to detect the
     failure of an EVC across the PW domain. Thus, network-driven alarms
     generated upon failure detection in the NS or PW domain and their
     mappings to the other domain are needed. There are also cases where
     a PE MAY not be able to process NS OAM messages received on the PW
     even when such messages are defined, as in Ethernet case,
     necessitating the need for fault notification message mapping
     between the PW domain and the NS domain.
     
     For Multi-Segment PWs (MS-PWs) [RFC5659], Switching PEs (S-PEs) are
     not aware of the NS. Thus, failure detection and notification at S-
     PEs will be based on PW OAM mechanisms. Mapping between PW OAM and
     NS OAM will be required at the Terminating PEs (T-PEs) to propagate
     the failure notification to the EVC endpoints.
     
     Similar to [RFC6310], the intent of this document is to standardize
     the behavior of PEs with respect to failures on Ethernet ACs and
     PWs, so that there is no ambiguity about the alarms generated and
     consequent actions undertaken by PEs in response to specific
     failure conditions.
     
     
     
     
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     2.1. Reference Model and Defect Locations
     
     Figure 1 is the same as used in [RFC6310] and is reproduced in this
     document as a reference to highlight defect locations.
     
                 ACs             PSN tunnel               ACs
                        +----+                  +----+
        +----+          | PE1|==================| PE2|          +----+
        |    |---(a)---(b)..(c)......PW1..(d)..(e)..(f)---(g)---|    |
        | CE1|   (N1)   |    |                  |    |    (N2)  |CE2 |
        |    |----------|............PW2.............|----------|    |
        +----+          |    |==================|    |          +----+
             ^          +----+                  +----+          ^
             |      Provider Edge 1         Provider Edge 2     |
             |                                                  |
             |<-------------- Emulated Service ---------------->|
        Customer                                              Customer
        Edge 1                                                Edge 2
                Figure 1: PWE3 Network Defect Locations
     
     2.2.  Abstract Defect States
     
     Abstract Defect States are also introduced in [RFC6310]. This
     document uses the same conventions, as shown in Figure 2, from
     [RFC6310]. It may be noted however that CE devices, shown in Figure
     2, do not necessarily have to be end customer devices. These are
     essentially devices in client network segments that are connecting
     to the Packet Switched Network (PSN) for the emulated services.
     
                                     +-----+
                ----AC receive ----->|     |-----PW transmit---->
            CE1                      | PE1 |                    PE2/CE2
                <---AC transmit------|     |<----PW receive-----
                                     +-----+
       (arrows indicate direction of user traffic impacted by a defect)
     
         Figure 2: Transmit and Receive Defect States and Notifications
     
     The procedures outlined in this document define the entry and exit
     criteria for each of the four defect states with respect to
     Ethernet ACs and corresponding PWs, and the consequent actions that
     PE1 MUST support to properly interwork these defect states and
     corresponding notification messages between the PW domain and the
     Native Service (NS) domain. Receive Defect state SHOULD have
     precedence over Transmit Defect state in terms of handling, when
     both transmit and receive defect states are identified
     simultaneously.
     
     
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     Following is a summary of the defect states from the viewpoint of
     PE1 in Figure 2:
     
     - A PW receive defect at PE1 impacts PE1 ability to receive traffic
     on the PW. PW defect state entry and exit criteria are described in
     section 4.4.1.
     
     - A PW transmit defect at PE1 impacts PE1 ability to send user
     traffic toward CE2. PE1 MAY be notified of a PW transmit defect via
     Reverse Defect Indication from PE2, which could point to problems
     associated with PE2's inability to receive traffic on the PW or
     PE2's inability to transmit traffic on its local AC. PW transmit
     state defect entry and exit criteria are described in section
     4.4.2.
     
     - An AC receive defect at PE1 impacts PE1 ability to receive user
     traffic from the Client domain attached to PE1 via that AC. AC
     receive state entry and exit criteria are described in section 5.1
     
     - An AC transmit defect at PE1 impacts PE1 ability to send user
     traffic on the local AC. AC transmit defect state entry and exit
     criteria are described in section 5.2.
     
     3. Abbreviation and Terminology
     
     3.1. Abbreviations
     
        AIS   Alarm Indication Signal
        AC    Attachment Circuit
        BFD   Bidirectional Forwarding Detection
        CC    Continuity Check
        CCM   Continuity Check Message
        CE    Customer Equipment
        CV    Connectivity Verification
        E-LMI Ethernet Local Management Interface
        EVC   Ethernet Virtual Circuit
        LDP   Label Distribution Protocol
        LoS   Loss of Signal
        MA    Maintenance Association
        MD    Maintenance Domain
        ME    Maintenance Entity
        MEG   Maintenance Entity Group
        MEP   MEG End Point
        MIP   MEG End Point
        MPLS  Multiprotocol Label Switching
        MS-PW Multi-Segment Pseudowire
     
     
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        NS    Native Service
        OAM   Operations, Administration, and Maintenance
        PE    Provider Edge
        PSN   Packet Switched Network
        PW    Pseudowire
        RDI   means Remote Defect Indication when used in the context of
              CCM
        RDI   Reverse Defect Indication when used to semantically refer
              to defect indication in the reverse direction
        S-PE  Switching Provider Edge
        TLV   Type Length Value
        T-PE  Terminating Provider Edge
     
     
     3.2. Terminology
     
     This document uses the following terms with corresponding
     definitions:
     
        - MEG Level: identifies a value in the range of 0-7 associated
        with Ethernet OAM frame. MEG Level identifies the span of the
        Ethernet OAM frame.
     
         - MEP:    MEG End Point is responsible for origination and
        termination of OAM frames for a given MEG.
     
         - MIP:      MEG Intermediate Point is located between peer
        MEPs and can process OAM frames but does not initiate or
        terminate them.
     
     Further, this document also uses the terminology and conventions
     used in [RFC6310].
     
     4. PW Status and Defects
     
     [RFC6310] introduces a range of defects that impact PW status. All
     these defect conditions are applicable for Ethernet PWs.
     
     Similarly, there are different mechanisms described in [RFC6310] to
     detect PW defects, depending on the PSN type (e.g., MPLS PSN, MPLS-
     IP PSN). Any of these mechanisms can be used when monitoring the
     state of Ethernet PWs. [RFC6310] also discusses the applicability
     of these failure detection mechanisms.
     
     
     
     
     
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     4.1. Use of Native Service (NS) Notification
     
     When a MEP is defined on the PE and associated with an Ethernet
     PW, the PE can use native service OAM capabilities for failure
     notifications. Options include:
     
         - Sending of AIS frames from the local MEP to the MEP on the
     remote PE when the MEP needs to convey PE receive defects, and when
     CCM transmission is disabled.
     
         - Suspension of CCM frames transmission from the local MEP to
     the peer MEP on the remote PE to convey PE receive defects, when
     CCM transmission is enabled.
     
         - Setting the RDI bit in transmitted CCM frames, when loss of
     CCMs from the peer MEP is detected or the PE needs to convey PW
     reverse defects.
     
     These NS OAM notifications are inserted into the corresponding PW.
     
     Similarly, when the defect conditions are cleared, a PE can take
     one of the following actions, depending on the mechanism that was
     used for failure notification, to clear the defect sate on the peer
     PE:
          - Stopping AIS frame transmission from the local MEP to the
     MEP on the remote PE to clear PW receive defects.
     
          - Resuming CCM frames transmission from the local MEP to the
     peer MEP on the remote PE to clear PW forward defects notification,
     when CCM transmission is enabled.
     
          - Clearing the RDI bit in transmitted CCM frames, to clear PW
     transmit defects notification, when CCM transmission is enabled.
     
     
     4.2. Use of PW Status Notification for MPLS PSNs
     
     When PWs are established using the Label Distribution Protocol
     (LDP), LDP status notification signaling MUST be used as the
     default mechanism to signal AC and PW status and defects [RFC4447].
     That is known as the "coupled loop mode". For PWs established over
     an MPLS or MPLS-IP PSN using other mechanisms (e.g. static
     configuration), inband signaling using VCCV-BFD [RFC5885] SHOULD be
     used to convey AC and PW status and defects.
     
     
     
     
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     [RFC6310] identifies the following PW defect status codepoints:
     
     
     
        - Forward defect: corresponds to a logical OR of local AC
        (ingress) Receive fault, local PSN-facing PW (egress) transmit
        fault, and PW not forwarding fault.
     
        - Reverse defect: corresponds to a logical OR of local AC
        (egress) transmit fault and local PW PSN-facing (ingress)
        receive fault.
     
     There are also scenarios where a PE carries out PW label withdrawal
     instead of PW status notification. These include administrative
     disablement of the PW or loss of Target LDP session with the peer
     PE.
     
     4.3. Use of BFD Diagnostic Codes
     
     When using VCCV, the control channel (CC) type and Connectivity
     Verification (CV) Type are agreed on between the peer PEs using the
     VCC parameter field signaled as a sub-TLV of the interface
     parameters TLV when using FEC 129 and the interface parameter sub-
     TLV when using FEC 128.
     
     As defined in [RFC6310], when CV type of 0x04 0r 0x10 is used to
     indicate that BFD is used for PW fault detection only, PW defect is
     detected via the BFD session while other defects, such as AC defect
     or PE internal defects preventing it from forwarding traffic, are
     communicated via LDP Status notification message in MPLS and MPLS-
     IP PSNs or other mechanisms in L2TP-IP PSN.
     
     Similarly, when CV type of 0x08 or 0x20 is used to indicate that
     BFD is used for both PW fault detection and AC/PW Fault
     Notification, all defects are signaled via BFD.
     
     4.4. PW Defect States Entry and Exit Criteria
     
     4.4.1. PW Receive Defect State Entry and Exit
     
     As described in [RFC6310] section 6.2.1, PE1 will enter the PW
     receive defect state if one or more of the following occurs:
     
        - It receives a forward defect indication (FDI) from PE2
     indicating either a receive defect on the remote AC or that PE2
     detected or was notified of downstream PW fault.
     
     
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       - It detects loss of connectivity on the PSN tunnel upstream of
     PE1, which affects the traffic it receives from PE2.
     
       - It detects a loss of PW connectivity through VCCV-BFD, VCCV-
     PING, or NS OAM mechanisms (i.e., CC) when enabled, which affects
     the traffic it receives from PE2.
     
     Note that if the PW LDP control session between the PEs fails, the
     PW is torn down and needs to be re-established.  However, the
     consequent actions towards the ACs are the same as if the PW
     entered the receive defect state.
     
     PE1 will exit the PW receive defect state when the following
     conditions are met.  Note that this may result in a transition to
     the PW operational state or the PW transmit defect state.
     
        - All previously detected defects have disappeared
        - PE2 cleared the FDI, if applicable
     
     
     4.4.2. PW Transmit Defect State Entry and Exit
     
     PE1 will enter the PW transmit defect state if the following
     conditions occur:
     
        - It receives a Reverse Defect Indication (RDI) from PE2
        indicating either a transmit fault on the remote AC or that PE2
        detected or was notified of an upstream PW fault.
     
        - It is not already in the PW receive defect state.
     
        PE1 will exit the transmit defect state if it receives an OAM
        message from PE2 clearing the RDI, or it has entered the PW
        receive defect state.
     
     5. Ethernet AC Defect States Entry and Exit Criteria
     
     5.1. AC Receive Defect State Entry and Exit
     
     PE1 enters the AC Receive Defect state if any of the following
     conditions is met:
     
     - It detects or is notified of a physical layer fault on the
     Ethernet interface. Ethernet link failure can be detected based on
     loss of signal (LoS) or via Ethernet Link OAM [802.3] critical link
     
     
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     event notifications generated at an upstream node CE1 with "Dying
     Gasp" or "Critical Event" indication, or via a client Signal Fail
     message [Y.1731].
     
     - A MEP associated with the local AC receives an Ethernet AIS frame
     from CE1.
     
     - A MEP associated with the local AC does not receive CCM frames
     from the peer MEP in the client domain (e.g. CE1) within an
     interval equal to 3.5 times the CCM transmission period configured
     for the MEP. This is the case when CCM transmission is enabled.
     
     - A CCM with interface status TLV indicating interface down. Other
     CCM interface status TLVs will not be used to indicate failure or
     recovery from failure.
     
     It should be noted when a MEP at a PE or a CE receives a CCM with
     the wrong MEG ID, MEP ID, or MEP level, the receiving PE or CE
     SHOULD treat such an event as an AC receive defect. In any case, if
     such events persist for 3.5 times the MEP local CCM transmission
     time, loss of continuity will be declared at the receiving end.
     
     PE1 exits the AC Receive Defect state if all of the conditions that
     resulted in entering the defect state are cleared. This includes
     all of the following conditions:
     
     - Any physical layer fault on the Ethernet interface, if detected
     or notified previously is removed (e.g., loss of signal (LoS)
     cleared, or Ethernet Link OAM [802.3] critical link event
     notifications with "Dying Gasp" or "Critical Event" indication
     cleared at an upstream node CE1).
     
     - A MEP associated with the local AC does not receive any Ethernet
     AIS frame within a period indicated by previously received AIS, if
     AIS resulted in entering the defect state.
     
     - A MEP associated with the local AC and configured with CCM
     enabled receives a configured number (e.g., 3 or more) of
     consecutive CCM frames from the peer MEP on CE1 within an interval
     equal to a multiple (3.5) of the CCM transmission period configured
     for the MEP.
     
      - CCM indicates interface status up.
     
     
     
     
     
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     5.2. AC Transmit Defect State Entry and Exit
     
     PE1 enters the AC Transmit Defect state if any of the following
     conditions is met:
     
     - It detects or is notified of a physical layer fault on the
     Ethernet interface where the AC is configured (e.g., via loss of
     signal (LoS) or Ethernet Link OAM [802.3] critical link event
     notifications generated at an upstream node CE1 with "Link Fault"
     indication).
     
     - A MEP configured with CCM transmission enabled and associated
     with the local AC receives a CCM frame, with its RDI (Remote Defect
     Indication) bit set, from the peer MEP in the client domain (e.g.,
     CE1).
     
     PE1 exits the AC Transmit Defect state if all of the conditions
     that resulted in entering the defect state are cleared. This
     includes all of the following conditions:
     
     - Any physical layer fault on the Ethernet interface, if detected
     or notified previously is removed (e.g., LOS cleared, Ethernet Link
     OAM [802.3] critical link event notifications with "Link Fault"
     indication cleared at an upstream node CE1).
     
     - A MEP configured with CCM transmission enabled and associated
     with the local AC does not receive a CCM frame with RDI bit set,
     having received a previous CCM frame with RDI bit set from the peer
     MEP in the client domain (e.g. CE1).
     
     6. Ethernet AC and PW Defect States Interworking
     
     6.1. PW Receive Defect Entry Procedures
     
     When the PW status on PE1 transitions from working to PW Receive
     Defect state, PE1's ability to receive user traffic from CE2 is
     impacted. As a result, PE1 needs to notify CE1 about this problem.
     
     Upon entry to the PW Receive Defect state, the following MUST be
     done:
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is not enabled, the MEP associated with the AC
     MUST transmit AIS frames periodically to the peer MEP in the client
     domain (e.g., on CE1) based on configured AIS transmission period.
     
     
     
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     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, and the MEP associated with the AC
     is configured to support Interface Status TLV in CCM messages, the
     MEP associated with the AC MUST transmit CCM frames with Interface
     Status TLV as being down to the peer MEP in the client domain
     (e.g., on CE1).
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, and the MEP associated with the AC
     is configured to not support Interface Status TLV in CCM messages,
     the MEP associated with the AC MUST stop transmitting CCM frames to
     the peer MEP in the client domain (e.g., on CE1).
     
     - If PE1 is configured to run E-LMI [MEF16] with CE1 and if E-LMI
     is used for failure notification, PE1 MUST transmit E-LMI
     asynchronous STATUS message with report type Single EVC
     Asynchronous Status indicating that PW is Not Active.
     
     Further, when PE1 enters the Receive Defect state, it MUST assume
     that PE2 has no knowledge of the defect and MUST send reverse
     defect failure notification to PE2. For MPLS PSN or MPLS-IP PSN,
     this is done via either a PW Status notification message indicating
     a reverse defect; or via VCCV-BFD diagnostic code of reverse defect
     if VCCV CV type of 0x08 or 0x20 had been negotiated. When Native
     Service OAM mechanism is supported on PE1, it can also use the NS
     OAM notification as specified in Section 4.1.
     
     If PW receive defect is entered as a result of a forward defect
     notification from PE2 or via loss of control adjacency, no
     additional action is needed since PE2 is expected to be aware of
     the defect.
     
     6.2. PW Receive Defect Exit Procedures
     
     When the PW status transitions from PW Receive Defect state to
     working, PE1's ability to receive user traffic from CE2 is
     restored. As a result, PE1 needs to cease defect notification to
     CE1 by performing the following:
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is not enabled, the MEP associated with the AC
     MUST stop transmitting AIS frames towards the peer MEP in the
     client domain (e.g., on CE1).
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, and the MEP associated with the AC
     
     
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     is configured to support Interface Status TLV in CCM messages, the
     MEP associated with the AC MUST transmit CCM frames with Interface
     Status TLV as being Up to the peer MEP in the client domain (e.g.,
     on CE1).
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, and the MEP associated with the AC
     is configured to not support Interface Status TLV in CCM messages,
     the MEP associated with the AC MUST resume transmitting CCM frames
     to the peer MEP in the client domain (e.g., on CE1).
     
     - If PE1 is configured to run E-LMI [MEF16] with CE1 and E-LMI is
     used for fault notification, PE1 MUST transmit E-LMI asynchronous
     STATUS message with report type Single EVC Asynchronous Status
     indicating that PW is Active.
     
     Further, if the PW receive defect was explicitly detected by PE1,
     it MUST now notify PE2 about clearing of Receive Defect state by
     clearing reverse defect notification. For PWs over MPLS PSN or
     MPLS-IP PSN, this is either done via PW Status message indicating
     working; or via VCCV-BFD diagnostic code if VCCV CV type of
     0x08/0x20 had been negotiated. When Native Service OAM mechanism is
     supported on PE, it can also clear the NS OAM notification as
     specified in Section 4.1.
     
     If PW receive defect was established via notification from PE2 or
     via loss of control adjacency, no additional action is needed,
     since PE2 is expected to be aware of the defect clearing.
     
     6.3. PW Transmit Defect Entry Procedures
     
     When the PW status transitions from working to PW Transmit Defect
     state, PE1's ability to transmit user traffic to CE2 is impacted.
     As a result, PE1 needs to notify CE1 about this problem which has
     been detected by PE1.
     
     Upon entry to the PW Transmit Defect state, the following MUST be
     done:
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, the MEP associated with the AC
     MUST set the RDI bit in transmitted CCM frames or send status TLV
     with interface down to the peer MEP in the client domain (e.g., on
     CE1).
     
     
     
     
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     - If PE1 is configured to run E-LMI [MEF16] with CE1 and E-LMI is
     used for fault notification, PE1 MUST transmit E-LMI asynchronous
     STATUS message with report type Single EVC Asynchronous Status
     indicating that PW is Not Active.
     
     - If the PW failure was detected by PE1 without receiving reverse
     defect notification from PE2, PE1 MUST assume PE2 has no knowledge
     of the defect and MUST notify PE2 by sending FDI."
     
     
     6.4. PW Transmit Defect Exit Procedures
     
     When the PW status transitions from PW Transmit Defect state to
     working, PE1's ability to transmit user traffic to CE2 is restored.
     As a result, PE1 needs to cease defect notifications to CE1 and
     perform the following:
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, the MEP associated with the AC
     MUST clear the RDI bit in the transmitted CCM frames to the peer
     MEP or send status TLV with interface up to the peer MEP in the
     client domain (e.g., on CE1).
     
     - If PE1 is configured to run E-LMI [MEF16] with CE1, PE1 MUST
     transmit E-LMI asynchronous STATUS message with report type Single
     EVC Asynchronous Status indicating that PW is Active.
     
     - PE1 MUST clear the FDI to PE2, if applicable.
     
     
     
     6.5. AC Receive Defect Entry Procedures
     
     When AC status transitions from working to AC Receive Defect state,
     PE1's ability to receive user traffic from CE1 is impacted. As a
     result, PE1 needs to notify PE2 and CE1 about this problem.
     
     If the AC receive defect is detected by PE1, it MUST notify PE2 in
     the form of a forward defect notification.
     
     When NS OAM is not supported on PE1, and for PW over MPLS PSN or
     MPLS-IP PSN, forward defect notification is done via either PW
     Status message indicating a forward defect or via VCCV-BFD
     diagnostic code of forward defect if VCCV CV type of 0x08/0x20 had
     been negotiated.
     
     
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     When Native Service OAM mechanism is supported on PE1, it can also
     use the NS OAM notification as specified in Section 4.1.
     
     In addition to the above actions, PE1 MUST perform the following:
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, the MEP associated with the AC
     MUST set the RDI bit in transmitted CCM frames.
     
     6.6. AC Receive Defect Exit Procedures
     
     When AC status transitions from AC Receive Defect to working, PE1's
     ability to receive user traffic from CE1 is restored. As a result,
     PE1 needs to cease defect notifications to PE2 and CE1 and perform
     the following:
     
     - When NS OAM is not supported on PE1 and for PW over MPLS PSN or
     MPLS-IP PSN, forward defect notification is cleared via PW Status
     message indicating a working state; or via VCCV-BFD diagnostic code
     if VCCV CV type of 0x08 or 0x20 had been negotiated.
     
     - When Native Service OAM mechanism is supported on PE1, PE1 clears
     the NS OAM notification as specified in Section 4.1.
     
     - If PE1 is configured with a down MEP associated with the local AC
     and CCM transmission is enabled, the MEP associated with the AC
     MUST clear the RDI bit in transmitted CCM frames to the peer MEP in
     the client domain (e.g., on CE1).
     
     6.7. AC Transmit Defect Entry Procedures
     
     When AC status transitions from working to AC Transmit Defect,
     PE1's ability to transmit user traffic to CE1 is impacted. As a
     result, PE1 needs to notify PE2 about this problem.
     
     If the AC transmit defect is detected by PE1, it MUST notify PE2 in
     the form of a reverse defect notification.
     
     When NS OAM is not supported on PE1, in PW over MPLS PSN or MPLS-IP
     PSN, reverse defect notification is either done via PW Status
     message indicating a reverse defect; or via VCCV-BFD diagnostic
     code of reverse defect if VCCV CV type of 0x08 or 0x20 had been
     negotiated.
     
     When Native Service OAM mechanism is supported on PE1, it can also
     use the NS OAM notification as specified in Section 4.1.
     
     
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     6.8. AC Transmit Defect Exit Procedures
     
     When AC status transitions from AC Transmit defect to working,
     PE1's ability to transmit user traffic to CE1 is restored. As a
     result, PE1 MUST clear reverse defect notification to PE2.
     
     When NS OAM is not supported on PE1 and for PW over MPLS PSN or
     MPLS-IP PSN, reverse defect notification is cleared via either a PW
     Status message indicating a working state or via VCCV-BFD
     diagnostic code if VCCV CV type of 0x08 or 0x20 had been
     negotiated.
     
     When Native Service OAM mechanism is supported on PE1, PE1 can
     clear NS OAM notification as specified in Section 4.1.
     
     7. Security Considerations
     
     The OAM interworking mechanisms described in this document do not
     change the security functions inherent in the actual messages.  All
     generic security considerations applicable to PW traffic specified
     in Section 10 of [RFC3985] are applicable to NS OAM messages
     transferred inside the PW.
     
     Security considerations in Section 10 of [RFC5085] for VCCV apply
     to the OAM messages thus transferred.  Security considerations
     applicable to the PWE3 control protocol of [RFC4447] Section 8.2
     apply to OAM indications transferred using the LDP status message.
     
     Since the mechanisms of this document enable propagation of OAM
     messages and fault conditions between native service networks and
     PSNs, continuity of the end-to-end service depends on a trust
     relationship between the operators of these networks.  Security
     considerations for such scenarios are discussed in Section 7 of
     [RFC5254].
     
     8. IANA Considerations
     
     This document has no actions for IANA.
     
     9. Acknowledgments
     
     The authors are thankful to Samer Salam, Matthew Bocci and Yaakov
     Stein for their valuable comments.
     
     
     
     
     
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     10. References
     
     10.1. Normative References
     
     [RFC6310] "Pseudowire (PW) Operations, Administration, and
     Maintenance (OAM) Message Mapping", RFC 6310, July 2011.
     
     [Y.1731] "OAM Functions and mechanisms for Ethernet based
     networks", ITU-T Y.1731, May 2006.
     
     [802.1ag] "Connectivity Fault Management", IEEE 802.1ag, December
     2007.
     
     [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
     Requirement Levels", BCP 14, RFC 2119, March 1997.
     
     [RFC4447] "Pseudowire Setup and Maintenance using LDP", RFC4447,
     April 2006.
     
     [RFC5885] "Bidirectional Forwarding Detection (BFD) for the
     Pseudowire Virtual Circuit Connectivity Verification (VCCV)",
     RFC5885, June 2010.
     
     [802.3] "CDMA/CD access method and physical layer specifications",
     Clause 57 for Operations, Administration and Maintenance, 2005.
     
     [MEF16] "Ethernet Local Management Interface", Metro Ethernet Forum
     Technical Specification MEF16, January 2006.
     
     [RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
     Connectivity Verification (VCCV): A Control Channel for
     Pseudowires", RFC 5085, December 2007.
     
     10.2. Informative References
     
     [RFC3985] "Pseudo Wire Emulation Edge-to-Edge(PWE3) Architecture",
     RFC 3985, April 2005.
     
     [RFC5659] "An Architecture for Multi-Segment Pseudo Wire Emulation
     Edge-to-Edge", RFC5659, October 2009.
     
     [RFC5254] Bitar, N., Bocci, M., and L. Martini, "Requirements for
     Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3)", RFC 5254,
     October 2008.
     
     
     
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     11. Appendix A: Ethernet Native Service Management
     
     Ethernet OAM mechanisms are broadly classified into two categories:
     Fault Management (FM) and Performance Monitoring (PM). ITU-T Y.1731
     provides coverage for both FM and PM while IEEE 802.1ag provides
     coverage for a sub-set of FM functions.
     
     Ethernet OAM also introduces the concept of Maintenance Entity (ME)
     which is used to identify the entity that needs to be managed. An
     ME is inherently a point-to-point association. However, in case of
     a multipoint association, Maintenance Entity Group (MEG) consisting
     of different MEs is used. IEEE 802.1 uses the concept of
     Maintenance Association (MA) which is used to identify both point-
     to-point and multipoint associations. Each MEG/MA consists of MEG
     End Points (MEPs) which are responsible for originating OAM frames.
     In between the MEPs, there can also be MEG Intermediate Points
     (MIPs) which do not originate OAM frames however do respond to OAM
     frames from MEPs.
     
     Ethernet OAM allows for hierarchical maintenance entities to allow
     for simultaneous end-to-end and segment monitoring. This is
     achieved by having a provision of up to 8 MEG Levels (MD Levels)
     where each MEP or MIP is associated with a specific MEG Level.
     
     It is important to note that the common set of FM mechanisms
     between IEEE 802.1ag and ITU-T Y.1731 are completely compatible.
     
     The common FM mechanisms include:
     
        1) Continuity Check Messages (CCM)
     
        2) Loopback Message (LBM) and Loopback Reply (LBR)
     
        3) Linktrace Message (LTM) and Linktrace Reply (LTR)
     
     CCM messages are used for fault detection including misconnections
     and mis-configurations. Typically CCM messages are sent as
     multicast frames or Unicast frames and also allow RDI
     notifications. LBM/LBR are used to perform fault verification,
     while also allow for MTU verification and CIR/EIR measurements.
     LTM/LTR can be used for discovering the path traversed between a
     MEP and another target MIP/MEP in the same MEG. LTM/LTR also allow
     for fault localization.
     
     In addition, ITU-T Y.1731 also specifies the following FM
     functions:
     
     
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        4) Alarm Indication Signal (AIS)
     
     
     
     AIS allows for fault notification to downstream and upstream nodes.
     
     Further, ITU-T Y.1731 also specifies the following PM functions:
     
        5) Loss Measurement Message (LMM) and Reply (LMR)
     
        6) Delay Measurement Message (DMN) and Reply (DMR)
     
        7) 1-way Delay Message (1DM)
     
     While LMM/LMR is used to measure Frame Loss Ratio (FLR), DMM/DMR is
     used to measure single-ended (aka two-way) Frame Delay (FD) and
     Frame Delay Variation (FDV, also known as Jitter). 1DM can be used
     for dual-ended (aka one-way) FD and FDV measurements.
     
     
     Authors' Addresses
     
     Dinesh Mohan
     Nortel
     3500 Carling Ave
     Ottawa, ON K2H8E9
     Email: dinmohan@hotmail.com
     
     Nabil Bitar
     Verizon
     60 Sylvan Road
     Waltham, MA 02145
     Email: nabil.n.bitar@verizon.com
     
     Ali Sajassi
     Cisco
     170 West Tasman Drive
     San Jose, CA  95134, US
     Email: sajassi@cisco.com
     
     Simon Delord
     Alcatel-Lucent
     215 Spring Street
     Melbourne, Australia
     E-mail: simon.delord@gmail.com
     
     Philippe Niger
     
     
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     France Telecom
     2 av. Pierre Marzin
     22300 LANNION, France
     E-mail: philippe.niger@francetelecom.com
     
     Ray Qiu
     Juniper
     1194 North Mathilda Avenue
     Sunnyvale, CA 94089, US
     Email: rqiu@juniper.net
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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